A Chinese spy ship has been sailing in international waters off the coast of Alaska for several days, according to a report by the CNN.

According to the report the ship first arrived in the area shortly before the test of the Terminal High Altitude Area Defense (THAAD) missile defense system test off Alaska.

U.S. Navy Capt. Scott Miller, spokesperson for the North American Aerospace Defence Command, said the ship is believed to be a "communications" or "intelligence" vessel and confirmed it has been in the area for the last few days.

He did not speculate over the reason for the presence of the ship.

Meanwhile, some officials pointed out that the Chinese ship is operating legally and said the U.S. does not have security concerns about the vessel.